The invention relates to casing hangers and in particular to a support collect for mudline-type hangers.
Mudline suspension systems are used to provide a means to hang off well bore casing strings below the ocean mudline during drilling. This avoids a need to build an offshore structure to accept the string weights and permits one to abandon the well temporarily until area exploration or all drilling of that location is completed.
As drilling in offshore applications tends toward deeper production zones, the casing hangers must carry additional weight. Deeper holes require more and longer strings to complete the well. Increasing wall sections to deal with the higher pressure compound suspension problems with heavier string weights and reduced annular area to work in. The annular area must be effectively divided between suspension and circulation (for cementing purposes) requirements.
Prior art hangers have used locking rings. These rings are secured to the inner casing and are continuously urged outwardly. They collapse sufficiently to pass through the casing bore and include latches on the rings which are formed to match receiving grooves in the outer casing at the support elevation. Releasable retaining means such as shear pins are sheared by the weight of the casing when the latches lock into the grooves. The inner casing is then lowered so that its shoulder rests on the ring.
One form of prior art ring illustrated in U.S. Pat. No. 3,893,717 is a C-shape with a section necessarily removed to allow it to collapse circumferentially to a point that it will pass thru the bore of the casing used above the hanger housing in the preceeding string. The C-shape ring requires a substantial wall section to provide a load carrying area for the "ring to housing" interface (seat) and also a load carrying area for the ring to hanger support, (top of the C-shape ring). Being that the hanger body must be able to drift thru the casing, these load carrying areas must be in two distinct radial planes.
To increase flexibility of the C-shape ring and avoid permanent deformation, additional parts of the wall section at selected points around the circumference must be removed. This removes bearing surface, in addition to that removed to permit collapse.
Another form also shown in U.S. Pat. No. 3,893,717 uses separate dogs urged outwardly by an internal C-member.
Still another form shown in U.S. Pat. No. 4,139,059 uses fingers which are cantilevered upwardly from a lower ring.